This invention relates to vehicle seat adjustment mechanisms and more particularly to a sensing device for sensing the position of a vehicle seat along a track.
Automobiles are normally designed with both front and rear seats. The front seat usually must be moved forward and the seat back tilted forward to provide access to the rear seating area in two door vehicle designs. It is well known in the art to provide vehicle seats which are manually adjustable forward and backward to suit the convenience of the occupant. Various powered mechanical mechanisms have also been designed to perform these adjustments. These power seat adjusters include a motor drive unit which can manually be energized in a forward or reverse direction to move the vehicle seat forward or backward.
A variety of mechanisms have been designed to also act as memory devices used in returning the vehicle seat to the original adjusted position in powered seat adjustment mechanisms. Examples of such mechanisms are disclosed in U.S. Pat. Nos. 3,183,314, 4,304,386, 3,250,566 and 4,283,036. These patents teach mechanical mechanisms utilizing program wheels, cams and limit switches.
All of these mechanisms are relatively complex arrangements of switches, cams, linkages and springs which may be prone to failure. In addition, difficulties with power seat systems which use mechanical indication devices to provide a "memory" of seat position, are related to gear backlash, drive cable windup and release, and speed variations which can all play a part in limiting the accuracy of positioning as well as the repeatability of the mechanism. Accordingly, there is a need for a simple and inexpensive mechanism to provide accurate relative position information for a motorized or powered seat adjustment mechanism.
It is therefore an object of the present invention to provide a simple, inexpensive position sensing device that essentially uses only two basic components, a magnetic strip and a magnetic field sensor. It is another object of the present invention to provide a vehicle position sensing device which eliminates the sensitivity to mechanical uncertainties discussed above with respect to mechanical linkage assemblies.
The digital position sensor according to the present invention includes a Hall effect integrated circuit which, when passed through a changing magnetic field, causes its output transistor to turn on or turn off depending on the transitional direction of the changing magnetic field. The changing field is provided by a strip of small alternating magnetic poles which moves relative to the face of the Hall sensor. The relative motion between the magnetic strip and the Hall sensor may either be produced by moving the Hall sensor or moving the magnetic strip.
In one preferred embodiment, the magnetic strip is held stationary alongside the seat track upon which the vehicle seat assembly slides, and the Hall integrated circuit is maintained in a fixed position with respect to the vehicle seat assembly itself. As the vehicle seat is moved forward or backward along the track, the sensor is in turn moved along the face of the magnetic strip. As the Hall integrated circuit passes changing poles, a square wave current pulse is produced which is in turn fed to a control module which digitally counts the pulses and hence provides a direct indication of relative vehicle seat position.
Other objects, features and advantages of the present invention will become more apparent to those skilled in the art as the nature of the invention is better understood from the accompanying drawing and the following detailed description as well as the accompanying claims.